Keep track of which ancestors are needed to merge a change

This way we can more easily identify them to the web
frontend so users can locate the changes more quickly.

Signed-off-by: Shawn O. Pearce <sop@google.com>

mgrapp/src/com/google/codereview/manager/merge/CodeReviewCommit.java

@@ -19,6 +19,8 @@ import com.google.codereview.internal.PostMergeResult.MergeResultItem;
 import org.spearce.jgit.lib.AnyObjectId;
 import org.spearce.jgit.revwalk.RevCommit;
 
+import java.util.List;
+
 /** Extended commit entity with code review specific metadata. */
 class CodeReviewCommit extends RevCommit {
   /**
@@ -45,6 +47,9 @@ class CodeReviewCommit extends RevCommit {
    */
   MergeResultItem.CodeType statusCode;
 
+  /** Commits which are missing ancestors of this commit. */
+  List<CodeReviewCommit> missing;
+
   CodeReviewCommit(final AnyObjectId id) {
     super(id);
   }

mgrapp/src/com/google/codereview/manager/merge/MergeOp.java

@@ -17,6 +17,7 @@ package com.google.codereview.manager.merge;
 import com.google.codereview.internal.PendingMerge.PendingMergeItem;
 import com.google.codereview.internal.PendingMerge.PendingMergeResponse;
 import com.google.codereview.internal.PostMergeResult.MergeResultItem;
+import com.google.codereview.internal.PostMergeResult.MissingDependencyItem;
 import com.google.codereview.internal.PostMergeResult.PostMergeResultRequest;
 import com.google.codereview.manager.Backend;
 import com.google.codereview.manager.InvalidRepositoryException;
@@ -381,6 +382,21 @@ class MergeOp {
     final MergeResultItem.Builder delay = MergeResultItem.newBuilder();
     delay.setStatusCode(c.statusCode);
     delay.setPatchsetKey(c.patchsetKey);
+
+    if (c.statusCode == MergeResultItem.CodeType.MISSING_DEPENDENCY) {
+      for (final CodeReviewCommit m : c.missing) {
+        final MissingDependencyItem.Builder d;
+
+        d = MissingDependencyItem.newBuilder();
+        if (m.patchsetKey != null) {
+          d.setPatchsetKey(m.patchsetKey);
+        } else {
+          d.setRevisionId(m.getId().name());
+        }
+        delay.addMissing(d);
+      }
+    }
+
     return delay.build();
   }
 }

mgrapp/src/com/google/codereview/manager/merge/MergeSorter.java

@@ -22,6 +22,7 @@ import org.spearce.jgit.revwalk.RevFlag;
 import org.spearce.jgit.revwalk.RevWalk;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -42,7 +43,7 @@ class MergeSorter {
       throws IOException {
     final Set<CodeReviewCommit> heads = new HashSet<CodeReviewCommit>();
     final Set<CodeReviewCommit> sort = prepareList(incoming);
-    INCOMING: while (!sort.isEmpty()) {
+    while (!sort.isEmpty()) {
       final CodeReviewCommit n = removeOne(sort);
 
       rw.resetRetain(CAN_MERGE);
@@ -58,10 +59,18 @@ class MergeSorter {
           // We cannot merge n as it would bring something we
           // aren't permitted to merge at this time. Drop n.
           //
-          n.statusCode = MergeResultItem.CodeType.MISSING_DEPENDENCY;
+          if (n.missing == null) {
-          continue INCOMING;
+            n.statusCode = MergeResultItem.CodeType.MISSING_DEPENDENCY;
+            n.missing = new ArrayList<CodeReviewCommit>();
+          }
+          n.missing.add((CodeReviewCommit) c);
+        } else {
+          contents.add(c);
         }
-        contents.add(c);
+      }
+
+      if (n.statusCode == MergeResultItem.CodeType.MISSING_DEPENDENCY) {
+        continue;
       }
 
       // Anything reachable through us is better merged by just

proto/internal/post_merge_result.proto

@@ -15,6 +15,18 @@
 package codereview.internal;
 option java_package = "com.google.codereview.internal";
 
+message MissingDependencyItem {
+  // Unique key of the PatchSet that is missing; missing
+  // if the patchset is not known but the revision is.
+  //
+  optional string patchset_key = 1;
+
+  // Unique revision id of the revision that is missing,
+  // if patchset_key was not available to the processor.
+  //
+  optional string revision_id = 2;
+}
+
 message MergeResultItem {
   enum CodeType {
     CLEAN_MERGE = 1;        // change merged clean
@@ -27,6 +39,11 @@ message MergeResultItem {
   // Unique key of the PatchSet to merge
   //
   required string patchset_key = 2;
+
+  // If status_code = MISSING_DEPENDENCY this is the list of
+  // ancestors needed to merge this item into the branch.
+  //
+  repeated MissingDependencyItem missing = 3;
 }
 
 message PostMergeResultRequest {